Effect of site directed mutagenesis in the CMGCC region of the alpha-subunit on immunoreactive human thyrotropin.

The cDNA of the common alpha-subunit of human glycoprotein hormone was mutated by site directed mutagenesis in the CMGCC region composed of cysteine-methionine-glycine-cysteine-cysteine (position 28-32). The cDNA of wild-type human thyrotropin (hTSH) beta-subunit and that of wild-type or mutant common alpha-subunits were co-transfected into COS-I cells. The concentration of hTSH determined by two immunoradiometric assay systems was detectable in culture media of COS-I cells transfected with wild-type (CMGCC) and a mutant (CRGCC) alpha-subunits but not four other mutants (YMGCC) (CMRCC) (CMACC) (CMDCC). The present data with the other studies on wild-type or mutant glycoprotein hormones support our hypothesis that an amino acid motif of "C-X-G-X-C" in the common alpha-(CMGCC in human) and beta-(CAGYC in human) subunits play an important role in biosynthesis of glycoprotein hormones in all species.